1. Technical Field
This application relates to a self-centering hub for timing discs of encoders, stepping motors or spinning roller drives, comprising a hub plate for fixing a timing disc or a code carrier, and a slotted hub shank for being slipped on to the shaft end of an input or output unit as well as an annular clamping piece form-fittingly slid on to the hub shank.
2. Background Information
From German Patent No. 19860012A1 (PWB-Ruhlatec lndustrieprodukte GmbH) there is known a self-centering timing disc hub of the initially described type and a method of mounting same. Self-centering is achieved in that the outer wall of the hub shank is at least partially conical, with the cone angle rising from the shank end to the contact face of the timing disc. After the hub shank has been slipped onto the motor shaft, a clamping element, e.g. in the form of a ring, is slipped on to the cone, as a result of which the clamping effect of the slotted hub on the motor shaft is increased.
When mounting the timing disc hub care has to be taken to ensure that centering on the motor shaft takes place automatically, i.e. that it is a self-centering action. For this purpose, the hub shank, on its side facing the shaft end and the motor flange plane respectively, comprises a so-called “catching bore”. Furthermore, to achieve self-centering, there is required a certain amount of play and guidance between the motor shaft and the hub shank, so that the hub cannot be pushed on to the shaft at an angle, but is centered in the conically widening catching bore.
German Patent No. 10150705A1 (Bayerische Motorenwerke AG) describes a form fitting shaft/hub connection wherein, on the outside of the hub, there is arranged a pre-tensioning element which permits a tensile stress of the hub in the radial direction on the shaft. The pre-tensioning element has the function of a tensioning nut and is provided with a conical inner thread. It is not shown how the pre-tensioning element is secured in the tensioned position.
German Patent No. DE19737307A1 discloses a shrinking disc for connecting a shaft and hub. It consists of a tensioning sleeve with a conical outer face and of a tensioning ring with a conical inner face, with the conical outer face of the tensioning sleeve being provided with a conical thread which is made to engage a correspondingly formed inner thread of the tensioning ring. By rotating the tensioning sleeve and the tensioning ring, the shrinking disc is tightened. One hexagon each is arranged at the tensioning sleeve and at the shrinking disc to permit the correspondingly high torque values to be applied.
The use of self-centering hubs becomes more and more common in all technical fields, so that by now, very high production numbers are achieved. Under conditions of mass production, a problem is caused by the stringent requirements to be met in respect of the surface quality of motor shafts and timing disc hubs and in respect of production accuracy to be able to observe the required tolerances. Even a slight displacement or skew position of the timing disc relative to the motor shaft is sufficient for adversely affecting the functioning of servomotors, spinning roller drives or similar sensitive applications, thus increasing the quota of rejects.